An organic EL element consists basically of a lower electrode, an organic luminescent layer and a counter electrode. Then, the lower electrodes and the counter electrodes are matrixed so that pixels are formed at their intersections, with the result that a display can be formed by a plurality of arrays of pixels.
By the way, recent display devices utilizing the organic EL elements have a tendency toward high definition and large size. Thus, in order to realize the high definition, it is desired that the pixel size should be equal to or less than several hundreds of micron square.
In this case, scanning electrode lines and signal electrode lines constituting a display become finer, and accordingly the resistance may possibly go up to several K.OMEGA. or more. The high definition display has more than 100 scanning electrode lines and more than 100 signal electrode lines. In this case, the duty must be achieved with a pulse number which is equal to the reciprocal of the number of scanning electrode lines, so that a high current pulse flows across the scanning electrode lines. At that time, there arose a problem that a high resistance of the scanning electrode lines or signal electrode lines might cause a voltage drop attributable to the wiring or a delay in response upon the drive attributable to the electrode resistance. That is, the voltage drop resulted in uneven luminance of the display, whereas the delay in response upon the drive resulted in a restriction of display since the delay may make it difficult to provide a fast moving picture in case of the fabrication of a high definition display.
To overcome such problems, the following organic EL elements are for example proposed.
Japanese Patent Laid-open Pub. No. Hei4-82197 discloses an organic EL element having a transparent electrode connected to a metal line to reduce the resistance of the transparent electrode.
Japanese Patent Laid-open Pub. No. Hei5-307997 discloses an organic EL element also having a transparent electrode on which is disposed a metal with a small work function to reduce the resistance of the transparent electrode.
Japanese Patent Pub. No. Hei5-76155 discloses an example of use of an auxiliary metal film in the EL element. An insulating film is disposed especially on the auxiliary metal film to prevent a dielectric breakdown.
However, the organic EL elements disclosed in Japanese Patent Laid-open Pub. Nos. Hei4-82197 and Hei5-307997 suffered from a problem that steps formed by the auxiliary metal wire might often break the counter electrode to cause any display defect. Furthermore, because of the injection of infinitesimal electric charges from the metal wiring into the organic layer of the organic EL element, e.g., a hole injection layer, the so-called cross talk often occurred.
An inorganic EL element disclosed in Japanese Patent Pub. No. Hei5-76155 also entailed a problem that some steps were caused by the thickness of the auxiliary metal film and the insulating film, resulting in frequent occurrence of breakage in the counter electrode.
The present invention was conceived in view of the above problems. It is therefore the object of the present invention to provide an organic EL element capable of reducing the resistance value of the transparent electrode (lower electrode) and eliminating steps attributable to the wiring layer to prevent a possible breakage in the counter electrode as well as capable of preventing the occurrence of the cross talk.
It is another object of the present invention to provide, for use as a high definition and large size display device, an organic EL display device using the organic EL element having the above characteristics, capable of significantly reducing the resistance value of the scanning electrode lines to achieve a uniform luminescence.